Isolating decoupler

ABSTRACT

An isolator decoupler comprising a shaft ( 1 ), a pulley ( 2 ) journalled to the shaft, a torsion spring ( 10 ) engaged between the pulley and a carrier ( 9 ), the torsion spring loaded in an unwinding direction, a wrap spring ( 11 ) engaged between the carrier and the shaft, the wrap spring comprising a cylindrical inner portion ( 94 ) and a planar outer portion ( 93 ) connected by a tapered portion ( 155 ), and the inner portion frictionally engaged with the shaft in a winding direction.

FIELD OF THE INVENTION

The invention relates to an isolating decoupler, and more particularly,to an isolating decoupler comprising a wrap spring engaged between thecarrier and the shaft, the wrap spring comprising a cylindrical innerportion and a planar outer portion connected by a tapered portion, andthe inner portion frictionally engaged with the shaft in a windingdirection.

BACKGROUND OF THE INVENTION

Diesel engine use for passenger car applications is increasing due tothe benefit of better fuel economy. Further, gasoline engines areincreasing compression ratios to improve the fuel efficiency. As aresult, diesel and gasoline engine accessory drive systems have toovercome the vibrations of greater magnitude from crankshafts due toabove mentioned changes in engines.

Due to increased crankshaft vibration plus highacceleration/deceleration rates and high alternator inertia the engineaccessory drive system is often experiencing belt chirp noise due tobelt slip. This will also reduce the belt operating life.

Crankshaft isolators/decouplers and alternator decouplers/isolators havebeen widely used for engines with high angular vibration to filter outvibration in engine operation speed range and to also control beltchirp.

Representative of the art is U.S. Ser. No. 13/541,216 which discloses anisolator decoupler having a pulley temporarily engagable with an end ofthe wrap spring one way clutch in an unwinding direction whereby atemporary contact between the wrap spring one way clutch end and thepulley will temporarily diminish the frictional engagement of the wrapspring one way clutch from the shaft.

What is needed is an isolating decoupler comprising a wrap springengaged between the carrier and the shaft, the wrap spring comprising acylindrical inner portion and a planar outer portion connected by atapered portion, and the inner portion frictionally engaged with theshaft in a winding direction. The present invention meets this need.

SUMMARY OF THE INVENTION

The primary aspect of the invention is an isolating decoupler comprisinga wrap spring engaged between the carrier and the shaft, the wrap springcomprising a cylindrical inner portion and a planar outer portionconnected by a tapered portion, and the inner portion frictionallyengaged with the shaft in a winding direction.

Other aspects of the invention will be pointed out or made obvious bythe following description of the invention and the accompanyingdrawings.

The invention comprises an isolator decoupler comprising a shaft, apulley journalled to the shaft, a torsion spring engaged between thepulley and a carrier, the torsion spring loaded in an unwindingdirection, a wrap spring engaged between the carrier and the shaft, thewrap spring comprising a cylindrical inner portion and a planar outerportion connected by a tapered portion, and the inner portionfrictionally engaged with the shaft in a winding direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate preferred embodiments of the presentinvention, and together with a description, serve to explain theprinciples of the invention.

FIG. 1 is a perspective view of the device.

FIG. 2 is a cross-section view of the device.

FIG. 3 is a detail of the cross-section view of the device.

FIG. 4 is an exploded view of the device.

FIG. 5A is a perspective view of the interior of the device.

FIG. 5B is a perspective cross-sectional view of the device.

FIG. 6 is a back perspective view of the carrier.

FIG. 7 is a front perspective view of the carrier.

FIG. 8 is a perspective view of the wrap spring and the pulley.

FIG. 9 is a detail of the transition portion of the wrap spring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a perspective view of the device. FIG. 2 is a cross-sectionview of the device. Isolating decoupler 100 comprises a pulley 2 whichis journalled to a shaft 1 by a bearing 7. Thrust washer 3 is disposedbetween pulley 2 and end cap 5. Thrust washer 6 is disposed betweenpulley 2 and shaft 1. Torsion spring 10 is engaged between pulley 2 andcarrier 9. Wrap spring 11 is engaged between carrier and shaft 1. Thrustwasher 22 is disposed between carrier 9 and radial member 21 of shaft 1.Carrier 9 bears upon thrust washer 22 due to compression of torsionspring between carrier 9 and pulley 2. Carrier 9 and wrap spring 11comprise the one-way clutch assembly 50. FIG. 6 is a back perspectiveview of the carrier. FIG. 7 is a front perspective view of the carrier.

Pulley 2 is axially located on shaft 1 between thrust washers 3 and 6,and retained thereon by end cap 5. Upon installation of the device onthe shaft of an alternator (not shown), end cap 5 becomes sandwichedbetween an alternator bearing inner race and shaft 1. This axially fixesthe location of the inventive device 100 on the alternator shaft. Shaft1 can be threadably fastened to the alternator shaft.

FIG. 6 is a back perspective view of the carrier. FIG. 7 is a frontperspective view of the carrier. One-way clutch assembly 50 comprisescarrier 9 and wrap spring 11. Carrier 9 comprises a face 77. End 78 oftorsion spring 10 bears upon face 77. The other end 79 of torsion spring10 engages pulley 2.

Wrap spring 11 comprises an outer planar spiral coiled portion 93 and aninner cylindrical coiled portion 94, see FIG. 8. FIG. 8 is a perspectiveview of the wrap spring and the pulley. Planar outer portion 93 andcylindrical inner portion 94 are connected by a tangential portion 155.Portion 155 extends radially outward from and tangentially from innerportion 94. Portion 93 comprises coils having a radius which increasesradially outward such that the coils are stacked radially outward one onthe next in a radially outward spiraling manner, namely, the coils arecoplanar within a plane that extends normally to an axis of rotationA-A. Wrap spring end 85 is torque limiting and end 89 is for receivingtorque input.

Wrap spring 11 is engaged between carrier 9 and shaft 1. Wrap springportion 110 of inner portion 94 frictionally engages shaft surface 53 ofshaft 1. Wrap spring outer portion 93 engages carrier 9 in receivingportion 91.

In the inventive device, torque is transmitted from pulley 2 throughtorsion spring 10 through one-way clutch assembly 50 to shaft 1 in thedirection of rotation of pulley 2. Torque is transmitted by wrap spring11 in the winding direction. Torsion spring 10 is loaded in theunwinding direction. In the unloaded or overrunning direction end 78 maydisengage from face 77 or from pulley or both, although this is notpreferable since it can cause noise and damage to the device.

FIG. 9 is a detail of the transition portion of the wrap spring. Thelength of each zone in FIG. 9 is not to scale. Wrap spring 11 comprisesa variable cross-section along the axial length of the spring wire. Thevariable cross-section characteristic comprises three portions or zones:constant cross-section zone 110, variable or tapered cross-section zone120, and constant cross-section zone 130. The cross-sectional dimensionof zone 130 is approximately 1.5 mm×2.5 mm. The cross-sectionaldimension of zone 110 is approximately 0.6 mm×1.2 mm. The numericalvalues given in this specification are examples only and are notintended to limit the scope of the invention.

Zone 130 takes load from carrier 9 at end 89. Carrier 9 is in contactwith torsion spring 10 at contact face 77. Zone 130 is wound on aspiral. The spiral nature of zone 130 acts as an energy absorbinginterface. For example, as the pulley rotates the coils of zone 130partially wind and unwind depending on the direction of rotation oracceleration of the pulley. Zone 130 must be fully “wound up” beforefull torque is transmitted to shaft 1. In this way the wrap spring actsas a compliant member to isolate the alternator from shocks that may becaused by abrupt engine speed changes. This is also the manner in whichthe torsion spring operates, namely, to allow the alternator shaft tooverrun when an engine deceleration occurs.

Wrap spring 11 comprises constant cross-section zone 110 and variablecross-section zone 120. Zone 130 connects to zone 120 at portion 1213.Zone 120 connects to zone 110 at portion 1112. Zone 120 is taperedcomprising a cross-sectional dimension that varies from 1.5 mm×2.5 mm atportion 1213 to 0.6 mm×1.2 mm at portion 1112. This transition in crosssection occurs gradually from the end of zone 130 through tangentialportion 155 and continues through the next two to three coils of innerportion 94. FIG. 9 is a detail of the transition portion of the wrapspring.

Maximum torque for an alternator is in the range of 16-20 N-m. At theconnection point between tangential portion 155 and zone 120 operationaltension will generate approximately 16 to 20 N-m torque at zone 120. Atconnection 1120 between zone 120 and zone 110 operational tension willgenerate torque approximately 6.5 to 10 times less than the maximumtorque delivered by torsion spring 10.

For example, the tension in wrap spring 11 can be determined by thefollowing formula:

T1/T2=e^(μφ)

Where

T1/T2=tension ratio.

μ=coefficient of friction between wrap spring and shaft.

φ=angle of contact between wrap spring and shaft in radians.

For the given example, with a coefficient of friction of 0.12 and anangle of contact representing three coils 3*2*π=18.85; tension ratio is9.6. With a coefficient of friction of 0.10; the tension ratio is 6.6.In practical terms since the coefficient of friction may vary it isreasonable to expect the tension ratio to be in the range ofapproximately 6.5 to 10.

The reduced torque is due to zone 120 generating 17 to 18 N-m torque onshaft 1. At connection 1120 there remains a tensile load within zone 120that generates about 2 to 3 N-m torque in zone 110. The cross-sectionaldimension of zone 110 is approximately 0.6 mm×1.2 mm. Zone 110 comprises9-10 spring coils.

There is no interference or only a small interference between variablecross-section zone 120 and shaft 1. This means that variablecross-section zone 120 can only transmit 1 to 2 N-m torque throughfrictional engagement. Zone 110 works as a trigger or a switch forvariable cross-section zone 120. Zone 110 has an interference fit withshaft 1 to transmit 2-3 N-m of torque.

In normal operation end 85 of wrap spring 11 does not come into contactwith pulley 2. As the torque input through pulley 2 to the deviceincreases the relative distance between tab 68 of pulley 2 with respectto end 85 will decrease. Once contact occurs at a predetermined torqueinput, further pressing contact (caused by increasing torque) betweentab 68 and end 85 will cause wrap spring 11 to progressively disengagefrom shaft surface 53 thereby allowing pulley 2 to “slip” past shaft 1.This is because a further relative movement of tab 68 against end 85causes wrap spring 11 to move in the unwinding direction, whichincreases the diameter of wrap spring 11, which progressively andincrementally disengages wrap spring 11 from shaft surface 53. Thisprogressive or incremental contact causes the magnitude of thefrictional engagement between the wrap spring and the shaft to beincrementally reduced by the incremental pressure from the pulley. Asthe over-torque load increases the wrap spring is further and furtherunwound from the shaft, thereby allowing the pulley greater freedom toslip past the shaft, which in turn “bleeds” off the high torque. Thistorque release function protects the device and driven component from anover-torque situation.

Wrap spring 11 is made from a continuous piece of spring wire. Thespring wire is produced from a wire having an initial cross-sectionaldimension of 1.5 mm×2.5 mm, which is also the cross-section of zone 130.In order to obtain the variable cross section of zone 120 and thesmaller cross section of zone 110, each spring wire must be processed.The first step is to cut the spring wire to length. Next, multiplespring wires are loaded in a fixture such that they are parallel,oriented to rest on the 1.5 mm side. The spring wires are then gangground to obtain a taper from 2.5 mm to 1.2 mm of zone 120 and the 1.2mm dimension of zone 110. Next the spring wires are removed from thefixture and placed on a magnetic table oriented such that they areparallel and rest on the side formerly 2.5 mm in length (the newlyground 1.2 mm side).

The spring wires are then gang ground to obtain the second transitionfrom 1.5 mm to 0.6 mm along zone 120 and the final thickness of 0.6 mmfor zone 110. The machined spring wire is then processed on typicalspring manufacturing winding equipment into the wound shape of wrapspring 11.

Although a form of the invention has been described herein, it will beobvious to those skilled in the art that variations may be made in theconstruction and relation of parts without departing from the spirit andscope of the invention described herein.

We claim:
 1. A method of forming a spring wire comprising: cutting aspring wire having a cross-sectional dimension of 1.5 mm×2.5 mm to apredetermined length; loading multiple spring wires into a fixturewherein the spring wires are parallel and resting on the 1.5 mm side;gang grinding the spring wires to obtain a portion having taper from 2.5mm to 1.2 mm; removing the spring wires from the fixture and placingthem on a magnetic table so the spring wires are parallel and rest onthe 1.2 mm side; gang grinding the spring wires to obtain a secondportion having a taper from 1.5 mm to 0.6 mm; and winding each springwire into a final shape.
 2. The method as in claim 1, wherein: windingeach spring wire to comprise an inner portion and an outer portionconnected by a tangential portion; configuring the inner portion to becylindrical; configuring the outer portion to be coplanar; and thecoplanar portion being normally disposed to an axis A-A of the innerportion.
 3. A method of forming a spring wire comprising: cutting aspring wire having a rectangular cross-section to a predeterminedlength, the rectangular cross-section having a long side and a shortside; loading multiple spring wires into a fixture wherein the springwires are parallel and resting on the short side; gang grinding thespring wires to obtain a portion having taper of the long side dimensionto approximately 50% of the long side dimension; removing the springwires from the fixture and placing them on a magnetic table so thespring wires are parallel and rest on the long side; gang grinding theshort side of the spring wires to obtain a second portion having a taperto approximately 50% of the short side dimension, the short side taperedportion coextensive with the long side tapered portion; and winding eachspring wire into a final shape.